Efforts to relieve world-wide shortages of protein have included various bio-synthesis processes in which single cell protein (SCP) is obtained by the growth of one or another of a variety of microorganisms on various carbon-containing substrates.
The carbon energy substrates should be readily available, relatively cheap, uniform, and safe. Petroleum hydrocarbons have been employed as carbon energy source, but have faced practical difficulties in the lack of water-solubility and in the high consumption of molecular oxygen needed to assist in the microbial conversion. Other processes have centered on the use of oxygenated hydrocarbon derivatives as feedstocks due to their relative water-solubility and hence ease of handling in an aqueous ferment, and in the substantially reduced molecular oxygen requirements for the microbial conversion-growth process.
However, a limiting factor in the commercialization of single cell protein processes has been the necessity to control the ferment at relatively moderate cell densities, but but moderate yields of dried cells based on substrate consumed, and the consequent necessity to handle large amounts of total fermentation effluent liquor in order to recover the moderate amounts of SCP material. Handling large quantities of aqueous fermentation effluent liquor complicates concentration of the single cell protein product in such as centrifuges, as well as washing and drying steps.
Some processes in the past have concentrated on the culturing of bacteria because of the slightly higher crude protein contents of the cell as compared to the content obtainable from yeast in general. However, yeasts are widely available and relatively simply cultured. Yeast cells generally are slightly larger as compared to bacteria cells, and, hence, yeast cells tend to be more easily separated from the fermentation effluent liquor.
Discovery of means and methods to increase cell yields, and particularly to operate and maintain continuous production at high cell densities, would be highly desirable. The resultant handling of substantially less fermentation liquor effluent volume, for example, would mean large savings in reduced sizes of piping and pumps, reduced makeup water requirements with reduced sterilization requirements, and reduced requirements of equipment sizing and handling for coagulation and separation processes.
Growth of yeast cells at high cell densities further allows more efficient assimilation of substrate in a smaller fermentation apparatus, useful, for example, in an effluent scrubbing scheme such as disclosed in U.S. Pat. No. 3,646,239. Yeast cells grown at high cell densities produce extracellular products in excellent yields, useful, for example, in an enhanced oil recovery process such as disclosed in U.S. Pat. No. 4,261,420, wherein a high cell density fermentation process will provide maximum CO.sub.2 production for oil recovery purposes. Other biochemical converstions using yeasts which can benefit from the high cell density fermentation process of my invention include the oxidation of alkanes to dicarboxylic acids (U.S. Pat. No. 3,796,630), the oxidation of C.sub.14 to C.sub.18 1-alkenes to epoxides and glycols Fonken, G. S., and R. A. Johnson, Chemical Oxidations With Microorganisms (Dekker, N.Y., 1972) pp 113-115, the oxidation of alcohols to ketones (U.S. Pat. No. 4,250,259, U.S. Pat. No. 4,268,630 and U.S. Pat. No. 4,269,940), and the production of extracellular biopolymers for use as viscosifying agents in aqueous media, e.g. in oil field water flooding applications (U.S. Pat. No. 3,312,279); the disclosures of all of these patents/articles being herein incorporated in total by reference, since all are amenable to improvement by my high salts feed/high cellular density fermentation method.